Wheel speed sensors have received increasing attention with the renewed interest in antilock braking systems. Almost all wheel speed sensors incorporate a sensor ring, often a toothed steel ring, that turns one-to-one with the wheel, and a pickup sensor facing the toothed ring. The pickup sensor is generally mounted stationary relative to the vehicle, since it has lead wires. Exactly where to mount the rotating sensor ring and the stationary sensor is a matter of design choice. The sensor ring may be mounted to a shaft that turns one-to-one with the wheel, and the sensor hung on a bracket fixed to the vehicle body. Such a system is generally not sealed from the environment. The vehicle wheel is always associated with a rolling bearing, which has one race that rotates at wheel speed and one that is stationary. Such a bearing may be part of the differential, or may be the bearing that directly mounts the wheel to the vehicle. Such bearings also generally have a sealed and protected interior annular space between the races, which contains the rolling bearing elements and their lubricant. When that annular space is large enough, one obvious expedient is to mount the sensor ring to the rotating race inside the sealed annular space, while inserting the sensor through the stationary race, or through a seal that is fixed to the stationary race. Thus, the sensor ring and sensor are sealed from the environment. The sensor may be made removable for easy post installation servicing, if desired. One such design is disclosed in USPN 3,719,841 to Ritsema.
A drawback of mounting components inside the bearing space is that removal of a component necessarily breaks the seal and exposes the bearing interior space to the environment, however briefly. Thus, wheel speed sensing has also been provided by mounting the components to the outside of the bearing. An extra seal or seals are provided to create a separate, dedicated sealed space for the sensor and sensor ring. One drawback of the exterior mounted approach is the extra expense involved in providing the extra seals necessary. However, the extra seal does keep bearing lubricant away from the sensor components, and allows the sensor to be pulled out without exposing the bearing to the environment. A more practical drawback is that the sensor components and extra seal may have to be shipped, handled and installed piecemeal to the bearing. An example of such an exterior mounted system with multiple components is disclosed in USPN 3,772,549 to Cumming.